Moving cleated crawler tracks in direct engagement with the ground operate in a well-known distinctive fashion from which small-scale ecosystems at ground level require a much higher degree of protection than from large tired wheels rolling over them. Rotation of the hoe base is accomplished by running the opposed parallel crawler tracks in opposite directions, and this motion always causes an oblique shearing action of cleats against any surface supporting the hoe. Frequent short to-and-fro adjustments of base location are in practice nearly as destructive because of the shearing action produced whenever traction is not perfect, which it seldom is.
The devising of what the Pacific Northwest logging industry now calls `hoe-chucking mats` raises design issues distinct from simple support issues addressed by devisors of mats for temporary roadways for wheeled traffic. The support capability of any matlike structure atop which equipment is operated is not a reliable indicator of the protection afforded to smallscale ecosystems under a hoe-chucking mat. From the industry perspective, hoe-chucking mats are increasingly important because heavy equipment accompanied by hoe-chucking mats is allowed to range more freely into natural areas where government regulations prohibit direct engagement of the ground by crawler track propulsion systems. If it `gets out` that mats are employed which do not effect the intended purpose of ecosystem protection, the next thing industry can expect is government imposed standardization of hoe-chucking mats. At present however, there are too few experts and too little research in this field, so I hope in my own way to advance the art by what I have devised with narrow focus on the special needs in hoe-chucking.
In hoe-chucking, the same crawler tracked equipment (hoe) from which the ground is to be protected is typically employed to pick up and shift a mat from location to location, in a leap-frogging manner. The hoe crawls onto its mat to take a new position from which the operator directs all the necessary work within reach of the boom.
Two `no-no` principles of hoe-chucking mat design I conceived after watching actual field operations are: (1) the topside of the mat should not have features which engage with the crawler track cleats in a manner transmitting forces tending to either destroy the mat or disturb the mat's placement; and (2) the underside of a hoe-chucking mat should not form a substantially airtight seal with the ground. The possibility of counter-rotation of a mat on wet ground, when the equipment base is rotated, is somewhat more readily grasped, perhaps, than the possibility that earth adhering to the underside of a mat will be pulled up with mat removal, but I saw both happen.
When the blanket-like strip of ground was pulled up with a mat, the base of the hoe working atop the mat for about twenty minutes had been repositioned frequently both by rotational and to-and-fro motions. In this case the mat position was not disturbed and the hoe pressed the mat into the underlying earth apparently quite evenly. Lacking a better term--what I call a `ground-seal` of the mat to the ground was formed. The removal of the mat was of course `no problem` to the operator of the powerful hoe, but the mat's removal caused extensive uprooting of the many small plants living at the location that had been `protected`. I do not believe anyone has addressed this problem before me.
In looking at mat design for hoe-chucking, I always consider whether or not the features of structure and arrangement in a mat really suit it to protecting ground level ecosystems in conditions of use--including the mat's removal. I refer to interaction of a mat with the ground below as `underside matters`, and with equipment above as `topside matters`. Mat design which does not address both underside and topside matters is not hoe-chucking mat design, in my opinion. Only because literature on the design issues of concern herein is apparently non-existent, I have turned to patents of certain mats which were devised specifically for one or the other of two applications: 1. temporary roadway mats; and 2. blasting mats. Mats of both categories are available in sizes making it tempting to adopt them as hoe-chucking mats.
Jerry Goldberg invented "a mat system for creating a temporary instant roadway surface over unstable ground" (claim phrasing), and was on Jul. 21, 1992 granted U.S. Pat. No. 5,131,787 for a TIRE MAT AND METHOD OF CONSTRUCTION. According to one version of his conception of using old tires in mats, he employs both a tire's (a.) sidewall portions, and (b.) tread portion, in the same product--a product which in my opinion deserves to be field-tested for possible application to hoe-chucking.
Assuming the orientation illustrated in FIG. 3, and addressing topside matters, I note that the wheel tires 27 of a vehicle traveling across the layer of overlapped sidewall portions 10, wired to one another by means W2, would not (because of the nature of the wheel tires) engage the means W2 in any severely detrimental way, even if the wheeled vehicle were moved in short to-and-fro motions on the mat. FIG. 2 depicts each pair of dual wheels 27 as straddling wiring means W2, but I hardly think such precision of driving is necessary; the mat could be run over from any direction by a wheeled vehicle without problems arising. However, the cleats of crawler tracks would in my opinion interact in a less harmless manner with overlapped tire sidewalls 10 interconnected by exposed W2s--keepinq in mind the rotational and to-and-fro motions of tracks in adjusting the base of a hoe working atop the same mat all day, often with rain supplying lubricant between the crawler track cleats and mat surface. Shearing action in this case is potentially damaging to things like twists of wire sticking up from a mat, no less than to plants sticking up from unprotected ground. The difference in toughness between a plant and a twist of wire is nothing to a powerful crawler track propulsion system--either can be sheared off.
The frequent handling of a hoe-chucking mat by means of powerful claws or clamshells on hoes is another point with regard to which the topside of Mr. Goldberg's mat leaves something to be desired.
Next, addressing underside matters, I note that Mr. Goldberg's tread portions 15 lie basically flat against the ground in FIG. 3. Referring to the end view presented by FIG. 2, rows of tread portions 15 lie in slightly deformed conforming contact with the ground. The illustrator commendably incorporated in FIG. 3 a realistic conformation of flexible structure with contours of the ground. Unfortunately neither Mr. Goldberg nor anyone else to my knowledge has said anything about what happens at the ground level when removing temporary road mats. Before anyone thinks a temporary road mat can be substituted for a hoe-chucking mat, because `a mat is a mat`, thought should first be given to what the road mat does to the ground when it fulfills the temporary function attributed to it, by being removed.
The proportionately quite narrow spaces shown in Mr. Goldberg's FIG. 2 between treads 15 would in hoe-chucking practice tend to become plugged with small plants and moist earth, causing there to be insufficient airway volume through his mat to ensure easy separation of mat and ground.
A tire mat according to the above-considered art possesses potential for hoe-chucking if overturned, and I believe that field tests both ways over would confirm this and all my foregoing analyses.
What happens to the ground in the case of blasting mats used for their intended purpose has often been closely studied by explosives engineers, but nothing to my knowledge has been published concerning their potential for hoe-chucking, though I know that some are being used. They are often conveniently ready-to-hand near hoe-chucking sites, since road building into the areas where small ecosystems require protection often involves extensive blasting.
Because blasting mats must be built to prevent upward passage through them of flyrock, most are designed without openings of a size larger than rock fragments thrown upwardly by a blast. To my way of thinking, and from what I have seen, the same absence of openings is to blame for their tendency to form an undesirable ground-seal when heavy equipment is operated atop them. There is, however, one particularly ingenius blasting mat known to me only from a perusal of patent literature which seems to diverge from our local practice in blasting mats, and which seems at first glance to solve the ground-seal problem--maybe, if so, affording a mat inherently of utility both for blasting and as a ground-protective hoe-chucking mat.
I refer to U.S. Pat. No. 3,793,953, BLASTING MAT, by Douglas L. Lewis., issued Feb. 26, 1974.
This clever Canadian invention is especially relevant to cite because of a superficial resemblance to my invention. The general similarity of appearance is encountered in the plan views (FIG. 1, Lewis, and FIG. 1, mine). But what Lewis really provides is "a mat constructed of a plurality of interleaved rectangular plates of resilient material arranged on edge in side-by-side spaced relationship in contiguous rows and strung together to secure the spaced plates in position in the mat while at the same time allowing movement of the edges of the plates when the mat is flexed to reduce the spacing between the plates." (Col. 1, lines 61-68, my underline) At Col. 3, lines 26-28, Lewis says, "It should also be noted the plates and spacers are sufficiently loose to permit the edges of plates 1 to move together . . . " (my underline)
Referring to FIGS. 5 and 6 illustrating the manner according to which Lewis's openings are closed in use, the edge movement of plates, mentioned above, is associated with a blast directed upwardly from beneath the mat. Because Lewis's "sufficiently loose" plates flex to close the openings, in the blasting application, I am of the opinion that when the force against them is the weight of overlying heavy equipment they will tend to close, still producing `V`-shaped recesses, but in this case inverted. Earth and small plants wedged into inverted `V`-shaped recesses would tend to be dug out and pulled from the ground, with removal of a Lewis mat used for hoe-chucking. In other words, the openings in mat structure provided by Lewis are not designed to be maintained open in the mat's intended use, and, because of the specified flexure and loose joining of elements also would not reliably be maintained open in hoe-chucking. The similar plan views are misleading if statically regarded, and in my opinion, this clever blasting mat by Lewis does not possess nearly the degree of potential an overturned Goldberg mat might have as a protective cover for ground level ecosystems, when crawler tracked heavy equipment is shifted about atop it.
A mat devised with utility both for hoe-chucking and blasting is an item I do not care to attempt in the present invention.